This invention relates to load creation apparatus, and to a method of testing the ability of a load bearing structure to bear a test mass that is created using such a load creation apparatus. The invention relates particularly, but not exclusively, to loads which are used for testing the load bearing characteristics of hoists, cranes, davits, winches and other load bearing structures. The invention also relates to the testing of static load bearing structures, such as foundation piles, bridges, floors, jetties and wharves.
Specifically, the invention does not relate or extend to containers and apparatus in general that are not adapted or designed for load creation and testing purposes.
The ability of a load bearing structure to bear maximum loads will decrease with its length of service, due to wear and tear of the apparatus. For this reason, it is necessary and sometimes mandatory that load bearing apparatus, such as hoists, cranes, davits and winches be tested periodically to verify that the apparatus are still capable of functioning at the maximum load capacity. In addition, such tests may be required when substantial alteration or repairs are made to the apparatus.
The tests require the load bearing structure or apparatus to successfully bear a specified test load or, more precisely, a test mass. Typically, test masses are in the range of a few metric tonnes to more than a few thousand metric tonnes and, in most cases, are in the range of 25% in excess of the safe working load of the load bearing structure or apparatus. Earlier test masses have been made of concrete or metal. Over a period of time, such test masses made of concrete can chip or crack and may thus loose their original precision of mass due to wear and tear. Metal objects will tend to rust, and may in some cases suffer from metal fatigue or crack propagation. Furthermore, these tests are conducted only periodically. It is appreciated that between tests, the storage of these solid test masses can create an inconvenient storage problem. Furthermore, the problem is exacerbated when a range of test masses, required for different apparatus, must be stored.
In response to the problems inherent in the use of solid test masses, the use of flexible liquid-filled bags as test masses has been proposed in United Kingdom Patent No. 2,047,414B (Tonnes Force Testing Services Limited) and United Kingdom Patent No. 2,072,351 (Water Weights Limited). The bags used in these British patents consist of flexible envelopes that are filled typically with water in order to create the necessary test mass. The liquid-filled bags resemble generally pear-shaped objects that are supported either singly or in combinations to create the specified test mass. Since these flexible bags are collapsible when empty, they solve the problem of storage that is inherent in the use of metal or concrete test masses. However, while one set of problems is overcome, the use of water or liquid weights introduces a different set of problems that is inherent in the use of temporary masses, namely the problem of ensuring that the bag is filled with the correct amount of liquid to create a mass of the correct value.
This problem of filling the bag accurately with the correct amount of liquid must be seen in the light of the fact that the standards of weight testing often require the masses to be within relatively fine tolerances. For example, reference is made to British Standard BS 7121 Part 2: 1991 which is entitled xe2x80x9cCode of practice for safe use of cranes. Part 2. Inspection, testing and examinationxe2x80x9d. According to British Standard BS 7121, the test mass should be of proven accuracy to within xc2x11.0%.
Another factor that presents difficulties in creating a temporary mass within the acceptable margins is that the density of a liquid varies with composition and temperature. Consequently, changes in the liquid density affect the mass. A cubic meter of pure water at 40xc2x0 C. weighs around 7.7 kg less than another cubic meter of water at 3.98xc2x0 C. The density of pure water at 40xc2x0 C. is around 992.3 kg mxe2x88x923, whereas at 3.98xc2x0 C. it is around 1000 kg mxe2x88x923. The density of sea water taken from the open sea may vary between approproximately 1020 and 1030 kg mxe2x88x923. When expressed as the amount of salt per kilogram of sea-water, in terms of parts per thousand by weight (o/oo), the salinity of sea-water varies typically from 34 to 37 o/oo and has been found to be as low as 5 o/oo in the Finland and as much as 41 o/oo in the northern part of the Red Sea. The difference of density in sea water is caused mainly by the variation in temperature and salinity. Fresh water and sea water are the most common liquids used to fill the weight testing bags. Hence, if a bag is filled consistently with the same amount of liquid, the vagaries of liquid density means that the bag may not necessarily contain the same mass on each occasion. These variables mean that the amount of liquid required to fill the bag is not constant, and must be ascertained in the context of the ambient conditions. These factors explain why the task of filling bags, with what can amount to thousands of liters of liquid, is not simple task, especially when the amount of liquid may have to be within xc2x11.0% of a specified amount as required by certain mandatory standards.
The vagaries discussed above mean that it is often necessary to weigh the mass using a weighing device such as a load cell or dynamometer. Although weighing the mass, at the time of using the test mass, can ensure that the vagaries of the amount of liquid and the prevailing density of the liquid are taken into account, the use of a weighing device, in turn, presents another set of problems. It is appreciated that the calibration (and indeed the maintenance of that calibration) of weighing devices used for masses in the range of a few thousand tonnes is expansive and not straightforward. Furthermore, the precision of the calibration is lost progressively over time, which means that the expensive process of calibration must be repeated regularly. For example, in British Standard BS 7121, the weighing device or weighbridge used to ascertain the value of the mass must, at the time of conducting the test, have been calibrated and certified within the last twelve months.
In the field of weight testing, the weighing devices usually include electrical components and circuitry. The use of such electrical weighing devices presents peculiar problems in applications where inflammable materials are in close proximity. For example, when testing cranes that are used in petroleum production facilities, it is necessary to ensure that the electrical weighing devices are shielded, so that any sparks from the weighing device will not initiate ignition of the petroleum products in the vicinity.
Another type of load bearing structure which must be tested with a test load is found in the piles used as a foundation of buildings. A test method is defined in A.S.T.M. D 1143-8 (American Society for Testing and Materials) which is entitled xe2x80x9cStandard Test Method for Piles Under Static Axial Compressive Load.xe2x80x9d After the foundation piles have been driven into the ground, the piles must be subjected to a static compressive load to test whether each pile has adequate load bearing capacity. The test loads are usually created by soil, rock, concrete, steel or water-filled tanks. These solid masses are usually solid, and are often in the form of large concrete blocks. Therefore, problems similar to the ones mentioned above in connection with solid test masses are experienced in transporting and positioning the large, solid masses on the test rig, and in storing the solid test masses when not in use. Furthermore, a weighing device in the form of a hydraulic jack is required to determine the actual test load, and this hydraulic jack must be regularly calibrated and certified. Other types of load bearing structures that must be tested with compressive loads include bridges, floors, jetties and wharves.
An object of the present invention is to overcome or substantially ameliorate at least some of the disadvantages of the prior art, and it is not intended that the invention in its broadest aspect must necessarily overcome all of the abovementioned problems in the prior art.
According to the present invention, there is provided a load creation apparatus operatively adapted to create a specified mass which is suitably large for load testing a load bearing structure, comprising:
a liquid impervious container;
means for filling the container with liquid to create the specified mass therein;
suspension means for suspending the container such that said load bearing structure is able to bear said specified mass; and
wherein the container is provided with determination means for determining the mass of the liquid which forms the specified mass in the container, the mass being determined from the density and volume of the liquid.
The determination means may be provided in the form of said container being substantially shaped as a regular geometric shape at least at those regions that are adjacent the liquid in the container such that the volume of liquid in said container is readily calculable.
The determination means may be provided in the form of said container being provided with walls which, in use, are upright at least at those regions that are adjacent the liquid in the container.
Preferably, the walls, in use, are generally vertical at least at those regions that are adjacent any liquid in the container.
The determination means may be provided in the form of said container being provided with a base that has a predetermined surface area.
The base may be orthogonal, and the base may be level.
The determination means may include a calibrated gauge which provides a visual indication of the level of liquid to which the container must be filled when the liquid has a particular density.
The visual indication may be adjustable in accordance with the density of the liquid.
The liquid impervious container may be made of flexible material.
The means for filling may be in the form of an opening for said container.
The means for emptying the container may be in the form of liquid discharge valve in the base of the container.
The suspension means may be in the form of a central strap which extends generally through the center of gravity of said container when liquid is in the container.
The container may be divided into partitions by an internal web that connects internal surfaces of the container, said web functioning as a structural brace for the container when the container contains liquid.
Liquid may be able to flow from one partition to an adjoining partition through vents located in the web.
Alternatively, the walls of the container may be provided with flat reinforcing components which enable the walls, in use, to remain upright.
Alternatively, or in addition to the reinforcing components, at least some of the walls of the container may be connected one to another with reinforcing struts, each of the struts functioning as a structural brace for the container when the container contains liquid.
According to another aspect of the invention, there is provided an arrangement for creating a specified mass for testing a load bearing structure comprising a plurality of load creation apparatus each of which are suspended, wherein said plurality of apparatus are juxtaposed with respect to one another.
The juxtaposed apparatus may be connectable by vents that enable at least one of the apparatus in the arrangement to be filled with liquid received from at least one other of said plurality of apparatus.
The vents may be in the form of a flexible duct that is able to interconnect adjacent apparatus.
The apparatus may be used for testing the ability of a load bearing structure to bear a specified test mass.
The arrangement may be used for testing the ability of a load bearing structure to bear a specified test mass.
According to a further aspect of the invention, there is provided a method of testing the ability of a load bearing structure to bear a suitably large specified test mass, comprising the steps of:
using suspension means to suspend at least one load creation apparatus such that the load bearing structure is able to bear a specified mass created by said load creation apparatus, said apparatus comprising a liquid impervious container;
filling said container with liquid to create said specified mass therein; and
using determination means provided on said container to determine said mass of the liquid which forms the specified mass in the container, the mass being determined from the volume and density of the liquid.
The method may involve the step of ascertaining the volume and density of the liquid and thereby determining the mass of the liquid therefrom.
Preferably, the determination means are provided in the form of said container being provided with walls which, in use, are upright at least at those regions that are adjacent the liquid in the container and said container being provided with a base that has a predetermined surface area, and wherein said method involves the step of calculating the volume of said liquid by multiplying the base surface area by the height of said liquid in the container and determining the value of the mass of the liquid therefrom.
The method may involve the step of ascertaining the density of liquid and thereby determining the amount of liquid with which to fill the container in order to produce the specified mass.
A plurality of said apparatus may be suspended in accordance with the abovementioned arrangement.
Liquid may be poured initially into one of said plurality of apparatus, and liquid from said one apparatus may flow to at least one other of said plurality of apparatus.
Preferably, one of more of said other apparatus are provided each with a valve which prevents the liquid from escaping from the apparatus such that the liquid is constrained to flow to at least one other of said apparatus until all the apparatus in the arrangement have been substantially filled to the required level.
The valve may be a float valve that is opened and closed by a floatable mechanism.
According to yet a further aspect of the invention, there is provided a load creation apparatus operatively adapted to create a specified mass which is suitably large for load testing a load bearing structure, comprising:
a liquid impervious container;
means for filling the container with liquid to create said specified mass therein; and
suspension means for suspending the container such that said load bearing structure is able to bear said specified mass;
wherein said container is provided with upright walls which are arranged and operatively adapted to determine the volume of the liquid therein, so that the specified mass created by the liquid in the container is able to be determined by reference to the density of the liquid.
The apparatus may be used for testing the ability of a foundation pile to bear a specified test mass.
The arrangement may be used for testing the ability of a foundation pile to bear a specified test mass.
The load bearing structure may be a hoist, crane, davit, winch or other similar load bearing structure.
In the specification and claims, it is said that the test mass is intended to be suspended such that a xe2x80x9cload bearing structurexe2x80x9d is able to bear the test mass. The word xe2x80x9cstructurexe2x80x9d is not intended to introduce any limitation on the type of structure, apparatus or machine that is able to be tested. For example, embodiments of the invention may be used for testing lifting machines such as hoists, cranes, davits and winches where the load is suspended from the apparatus. Other embodiments of the invention may be used to create a compressive load to be borne by load bearing structures such as structural foundation piles. The invention may be used to test a wide range of load bearing device which must be tested with a specified test mass.
In the specification, the word xe2x80x9cfilledxe2x80x9d is used in the descriptive sense of adding liquid to the container. The word xe2x80x9cfilledxe2x80x9d is not intended to imply that the container must necessarily be filled to the brim.